1. Field of the Invention
The present invention relates to a conversion device, particularly to a current-mode dual-slope temperature-digital conversion device.
2. Description of the Related Art
The daily-life appliances usually need temperature data, such as air conditioners, refrigerators, and fire warning systems. Temperature is measured via detecting the variation of a physical property, such as resistance variation, color variation, volume variation or electromotive force generated by magnetic flux change. The electric conductivity of a semiconductor material is greatly influenced by temperature. Therefore, the electric conductivity of an integrated circuit made of semiconductor materials correlates with temperature. The temperature characteristic curve of an integrated circuit is thus used to fabricate a temperature-sensing integrated circuit.
Refer to FIG. 1. A general temperature sensor comprises a temperature-dependent sensor 10, a reference source circuit 12 and an analog-to-digital converter (ADC) 14. The temperature-dependent sensor 10 generates temperature-dependent voltage or temperature-dependent current. The reference source circuit 12 generates temperature-independent reference voltage or temperature-independent reference current. The analog-to-digital converter 14 converts the voltage difference or current difference between the temperature-dependent sensor 10 and the reference source circuit 12 into digital signals.
The temperature sensors may be categorized into two systems: the voltage-domain system and the time-domain system. For the voltage-domain system, a complicated calibration circuit is needed to achieve high precision and high accuracy at a given operation voltage. The complicated calibration circuit should increase the time and cost of development, consume more power, and impair portability of products. The time-domain system is neither limited by voltage swing nor dependent on an additional calibration circuit. However, the time-domain system has some problems in the curvature of the conversion curve because the time-domain system adopts an inverter or a delay element as the temperature-dependent sensor.
Accordingly, the present invention proposes a current-mode dual-slope temperature-digital conversion device to overcome the abovementioned problems.